The present invention relates to an apparatus and method for purifying fluids including contaminants, and more particularly, to an apparatus and method for purifying fluids by eliminating airborne molecular contaminants(AMCs) with a photocatalyst.
During the fabrication of ULSI devices, the scale of integration of which is equal to or higher than 64 M (megabit) DRAMs, and the fabrication of LCD devices, fine contaminants that cannot be eliminated by a high performance filter (hereafter referred to as ultra low penetration air (ULPA) filter) may result in the fabrication of deficient ULSI and LCD devices.
The contaminants, which are airborne molecular contaminants, include, for example, organic gas and ammonia gas produced in the fabrication facility. The airborne molecular contaminants are eliminated by a purification apparatus, which uses an adsorbent formed from activated carbon, ion exchange resin, or the like.
FIG. 1 is a schematic diagram showing a prior art air purifier 91. The air purifier 91 is installed in, for example, the ceiling of a clean room, in which semiconductor devices are fabricated, to purify the air in the clean room.
The air purifier 91 includes a chemical filter 92, which eliminates airborne molecular contaminants, and an ULPA filter 93 for eliminating fine particles. A fan 94 is arranged between the chemical filter 92 and the ULPA filter 93. When the fan 94 is driven, the air in the clean room is drawn through the chemical filter 92 and the ULPA filter 93. This eliminates the airborne molecular contaminants and fine particles from the air. The purified air is then returned to the clean room.
The chemical filter 92 is formed by applying activated carbon or a reactive liquid (acid, base, catalyst component, or the like) based on activated carbon to a base material. When the adsorbed contaminant saturates the filter 92, the filter 92 must be replaced. Thus, new filters are needed, which requires maintenance procedures. In addition, the chemical filter 92, which is disposed of as waste, increases costs.
In comparison, a clean air purifier that uses a photocatalyst and does not produce waste is known. A typical photocatalyst is made of, for example, titanium dioxide(TiO2) and causes photocatalysis. In other words, when irradiated with ultraviolet rays, the photocatalyst is excited. This oxides and decomposes the airborne molecular contaminants. Air purifiers using a photocatalyst have recently been applied to normal household air-conditioners. In such air purifiers, the photocatalyst is irradiated with ultraviolet rays and air is drawn through the irradiated photocatalyst to decompose contaminants, such as material having an odor, that are suspended in air.
In the air purifier, ozone produced near the source of the ultraviolet rays mixes with the purified air. The ozone enhances oxidation at the surface of wafers used for semiconductor devices. Accordingly, an oxide film forms on a semiconductor wafer due to the ozone. This degrades the device characteristics, decreases the product quality, and decreases the yield.
Japanese Unexamined Patent Publication No. 10-234835 describes a second example of an air purifier in which a photocatalyst is included in an air filter. The air filter is mainly made of glass fiber. In this air purifier, the air filter is irradiated by a light source located in an air passage or located beside the air filter to excite the photocatalyst of the air filter and purify air.
However, in this air purifier, the ultraviolet rays irradiated from the light source are diffused in the air filter. Thus, the photocatalyst may not be excited at locations relatively far from the light source.
It is an object of the present invention to provide an apparatus and method for efficiently eliminating airborne molecular contaminants through photocatalysis without mixing ozone, which is produced by ultraviolet rays, in the treated fluid.
To achieve the above object, the present invention provides a purifying apparatus for purifying a fluid. The apparatus includes a fluid passage, through which the fluid flows, formed by an ultraviolet ray transmitting material, and a plurality of photocatalytic pipes arranged in the fluid passage. Each of the photocatalytic pipes has an inner surface and an outer surface on which a thin film of a photocatalyst is applied. The photocatalytic thin film is excited by ultraviolet rays irradiated from a location proximal to the fluid passage.
A second aspect of the present invention provides a purifying apparatus for purifying a fluid. The apparatus includes a fluid passage through which the fluid flows. A plurality of photocatalytic pipes are arranged in the fluid passage. Each of the photocatalytic pipes is inclined by a predetermined angle relative to a direction in which the fluid flows and has an inner surface on which a thin film of a photocatalyst is applied. The photocatalytic thin film is excited by ultraviolet rays irradiated from a location proximal to the photocatalytic pipes.
A third aspect of the present invention provides a method for purifying a fluid in a fluid passage. The method includes locating a plurality of photocatalytic pipes in the fluid passage. Each of the photocatalytic pipes has an inner surface and an outer surface to which a thin film of a photocatalyst is applied. The method also includes exciting the photocatalyst by irradiating the catalytic pipes with ultraviolet rays, and conveying the fluid through the fluid passage so that the fluid contacts the excited photocatalyst.